The present invention relates to a focal plane shutter for a still camera, and more particularly to a focal plane shutter including a novel shock absorption mechanism which effectively absorbs shock or oscillation upon the termination of the shutter operation and suitable for a high-speed shutter having a high blade speed.
A focal plane shutter for a recent camera, particularly a single lens reflex camera, attains the high-speed operation of shutter blades in order to maintain the exposure accuracy in a short exposure time and increase the strobo synchronization speed. A shutter of a vertical movement type, for example, was generally moved across a vertical distance of an aperture of 24 mm in about 7 ms several years ago, whereas it is adapted to be moved in about 3 ms recently.
As well known, in the focal plane shutter, shock or oscillation upon the termination of movement of the shutter blades is increased as the blade speed is increased. Further, it is also well known that the shock or oscillation causes large operation sound of the shutter and deterioration of the durability of the shutter. Accordingly, in order to reduce the operation sound of the shutter and improve the durability of the shutter, the focal plane shutter having a high blade speed is generally provided with a shock absorption mechanism for absorbing shock and oscillation upon the termination of movement of the shutter blades.
A conventional shock absorption mechanism which includes a rotatable brake lever held to be pressed between a friction plate and a leaf spring and disposed in a path through which a shutter blade driving member passes is generally known.
With such a shock absorption mechanism, when the blade driving member strikes against the brake lever, the brake lever is rotated while receiving friction between the friction plate and the leaf spring so that the kinetic energy of the blade driving member and the shutter blades is converted into the thermal energy generated by friction of the friction plate and the brake lever and accordingly shock upon the termination of movement of the shutter blades is absorbed.
However, the above-mentioned friction type shock absorption mechanism has many problems described below.
The coefficient of friction between the friction plate and the brake lever is affected by variation in temperature and accordingly the shock absorption performance is also affected by variation in temperature.
In addition, it is necessary to secure the space for disposing the shock absorbing brake lever and the friction mechanism near the space for disposing the driving mechanism for the shutter. Consequently, the space efficiency is reduced.
Further, since it is required to charge the shock absorption mechanism against the friction force at the same time when the shutter driving mechanism is charged, the charging force is increased.